1. Field of the Invention
This invention relates to contact lens manufacturing and in particular to a method for tracking contact lenses through a manufacturing line so that multiple stock keeping units (SKU) can be simultaneously fabricated on the same manufacturing line.
In known automated contact lens production processes a contact lens is formed by sandwiching a reaction mixture between two mold sections having respective concave and convex optical surfaces which define the lens. The reaction mixture is dispensed into the concave surface which forms the front curve of the lens and the second mold section is seated on the first mold section such that the convex surface which forms the back curve of the lens is placed over the concave surface to define a mold cavity between the concave and convex surfaces. The reaction mixture within the assembled mold is subject to a curing cycle which polymerises the monomer inside the mold cavity. Typical contact lens curing methods include UV radiation and/or thermal curing. Once the curing is complete, the mold sections are separated to reveal the lens which has formed therein.
The lens must pass through a series of further processing stages such as inspection, hydration, primary packaging, labelling, and secondary packaging in which multiple primary packages are housed in a box or carton each having one or more labels to identify its contents.
One type of contact lenses is commonly referred to as “spherical contact lenses”, i.e., contact lenses designed to provide a spherical optical correction (or “power”) to compensate for myopia (nearsightedness) or hypermetropia (farsightedness). Such contact lenses are also designed with fitting parameters, especially lens diameter and effective base curve. Accordingly, a prescription for a spherical contact lens will typically specify spherical correction (power), lens diameter and base curve. Using hydrogel lenses as an example, manufacturers typically market series of spherical hydrogel contact lenses, each series including lenses having common fitting parameters and offering powers in 0.25 or 0.50 diopter increments.
In addition to spherical lenses, there are contact lenses commonly referred to as “toric contact lenses”, i.e. contact lenses having a toric optical zone that are designed to correct refractive abnormalities of the eye associated with astigmatism. The toric optical zone provides cylindrical correction to compensate for the astigmatism, with the cylindrical correction commonly referred to as “cylindrical power”. The toric surface may be formed in either the posterior lens surface (back surface toric lens) or in the anterior lens surface (front surface toric lens). Whereas spherical contact lenses may freely rotate on the eye, toric contact lenses have some type of ballast to inhibit rotation of the lens on the eye is inhibited so that the cylindrical axis of the toric zone remains generally aligned with the axis of the astigmatism. For example, one or more sections of the lens periphery may be thicker (or thinner) than other sections to provide the ballast. Toric contact lenses are manufactured with a selected relationship (or offset) between the cylindrical axis of the toric optical zone and the orientation of the ballast. This relationship is expressed as the number of degrees (or rotational angle) that the cylindrical axis is offset from the orientation axis of the ballast; toric contact lens prescriptions specify this offset, with toric lenses generally being offered in 5 or 10-degree increments ranging from 0° to 180°.
Since astigmatism requiring vision correction is usually associated with other refractive abnormalities, such as nearsightedness or farsightedness, toric contact lenses are generally prescribed, in addition to cylindrical power and axes offset, with a spherical correction and fitting parameters as for the aforementioned spherical contact lenses. Accordingly, a prescription for toric contact lens will typically specify spherical correction (power), lens diameter, base curve, cylindrical correction, and axes offset. It will be appreciated that for each power of lens a manufacturer may offer a series of 36 lenses having different spherical correction. However, there may not be a need for a great number of any given lens configuration.
In the past many contact lens fabrication and packaging lines have been configured to produce one SKU of lenses at a time, each lens having the same predetermined optical characteristic, for example, all the lenses are +1 spherical power. As a result, a limited number of stocking units (SKUs) were produced in large SKU sizes. Changing production to a different SKU has required cleaning out the manufacturing line, and changing the molds. Changing the molds that are used in such systems have been attendant with machine downtime.
2. Description of Related Art
EP-A-1052084 addresses the need for greater numbers of SKUs in smaller SKUs by fabricating multiple, different SKUs without requiring that the manufacturing line be shut down and cleaned out, and avoids cross-contamination of the different SKUs.
It proposes a method for tracking multiple SKUs of ophthalmic devices in a manufacturing line, comprising the steps of:
assembling first molding devices at least one of said first molding devices having an identification means;
reading said identification means of said at least one of said first molding devices;
forming first molded parts using said first molding devices;
providing a plurality of carriers, said carriers having carrier indicators;
transferring said first molded parts to at least one of said plurality of carriers;
reading said carrier indicator of said at least one of said plurality of carriers carrying said first molded parts; and
storing in machine-accessible memory the information associated with said identification means of said at least one of said first molding devices and the information associated with said carrier indicator carrying said first molded parts. An apparatus for implementing the method is also disclosed.
While the proposed system is capable of tracking multiple SKUs, it relies upon placing the molding devices in carriers which carry them through the production line. This is not always desirable since conveying systems are capable of transporting assembled molds individually through and between manufacturing stages. Furthermore, in the cases of toric lenses the same mold pairs may be capable of producing a range of lenses of the same power having different spherical correction. Thus, identity of the mold pair is not sufficient to characterise the whole prescription and knowledge of the orientation of the mold halves relative to each other is required.